Materials Required
- Plastic bottle (clear)
- Water (can also use sparkling water)
- Vegetable oil
- Food coloring (water-soluble)
- Effervescent tablet (like Alka-Seltzer or antacid tablet)
Instructions
- Fill half of the bottle with water.
- Add several drops of food coloring to the water and mix well.
- Fill the rest of the bottle with vegetable oil.
- Tightly close the bottle.
- If the oil and water mixed, wait until they separate completely.
- Break an effervescent tablet into pieces and drop one piece into the bottle.
- Watch the colorful lava lamp effect!
- When the bubbling slows down, add another piece of tablet to restart the effect.
Tip: You can keep the bottle sealed and shake it gently to create different patterns, then let it settle and add more tablet pieces.
What's Happening?
Density and Separation:
The oil floats on top of the water because it is less dense (lighter) than water. The food coloring has the same density as water, so it sinks through the oil and mixes only with the water layer.
The Lava Effect:
When you add the effervescent tablet, it sinks to the bottom and starts to dissolve. As it dissolves, it produces carbon dioxide gas (CO2). Gas is lighter than water, so the bubbles float to the top.
The gas bubbles attach to colored water droplets and carry them up to the surface. When the bubbles reach the top and pop, releasing the gas into the air, the water droplets become heavy again and sink back down. This creates the mesmerizing lava lamp effect!
This cycle continues over and over until the tablet is completely dissolved.
Why Oil and Water Don't Mix
Oil and water are immiscible (they don't mix) because:
- Water molecules are polar (have positive and negative ends)
- Oil molecules are non-polar
- Similar molecules attract each other, so water stays with water and oil stays with oil